I once spent a few days trying to package up some python with Maven. It worked, but how many real advantages are there? A package manager is not a huge amount of code compared to e.g. a language standard library (and languages that reuse a standard library often do reuse the package manager). Even within a single ecosystem there are often multiple competing package managers, because people disagree about the right way to do things and often the best way to resolve this is to let them try and see how it turns out. And people derive value from having the package manager written in the same language they're developing in; it means they can extend or integrate it without having to learn a different language.

But a package manager that relies on Cygwin certainly isn't going to win. Most language-specific package managers are already doing better than that.